I am trying to obtain a reduction formula for ∫π/20(1−sin3x)ncosxdx
where n∈N. My attempt is as follows let v=sinx⟹dv=(cosx)dx
The integral then becomes ∫10(1−v3)ndv
By parts3n∫10v3(1−v3)n−1dv
But I can't get it in the form originally to have the integral exactly the same but in terms of n−1. Thanks in advance.
Answer
Continuing from where you left:
In=3n∫10v3(1−v3)n−1dv=3n(∫10(1−v3)n−1dv−∫10(1−v3)ndv)
⇒In=3n(In−1−In)⇒In=3n3n+1In−1
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